There are important applications for the type of receiver above-described, especially in the distribution of clock signals for large electronic systems such as computers, telephone exchanges, etc.
When transmitting digital data, it is necessary to synchronize the various systems and circuits involved, and for this purpose clock signals are transmitted for synchronization and auxiliary signals are transmitted for "frame" alignment, the data transmitted being assembled in blocks of data known as frames.
Several methods have been proposed for reducing the number of transmission lines required, e.g. by simultaneously transmitting both types of signal over the same line. The method of transmitting signals used in the present invention comprises including the auxiliary signals in the clock signals by periodically omitting a clock signal pulse. When F=kf, one pulse is omitted every k clock signal pulses in order to obtain the modified clock signals.
The waveforms are illustrated in FIG. 1 for the case k=4. The first waveform HC represents the clock signal, the second waveform HS represents the auxiliary signal, whilst the third waveform HM represents the modified clock signal.
In addition, for obvious reasons of dependability, the transmission circuit elements are conventionally tripled, transmitting the modified clock signals HM1, HM2 and HM3 over three transmission lines which are identical in every aspect. Such transmission devices require extremely high operational dependability, such that the failure of a single system component does not disable the system.
At the present time, it is necessary to increase the number of alarm devices when such a scheme is used, which raises problems of equipment size and cost.